You can now start
producing .NET Standard 2.0 libraries and NuGet packages. Please use
the latest .NET Core 2.0 Preview 2
as it contains many improvements that were necessary to provide a
good experience.

Details

Bigger API Surface:
We have more than doubled the set of available APIs from
13k in .NET Standard 1.6
to 32k in .NET Standard 2.0.
Most of the added APIs are .NET Framework APIs. These additions
make it much easier to port existing code to .NET Standard, and,
by extension, to any .NET implementation of .NET Standard, such
as .NET Core 2.0 and the upcoming version of UWP.

.NET Framework
compatibility mode: The vast majority of NuGet packages
are currently still targeting .NET Framework. Many projects are
currently blocked from moving to .NET Standard because not all
their dependencies are targeting .NET Standard yet. That's why
we added a compatibility mode that allows .NET Standard projects
to depend on .NET Framework libraries as if they were compiled
for .NET Standard. Of course, this may not work in all cases
(for instance, if the .NET Framework binaries uses WPF), but we
found that 70% of all NuGet
packages on nuget.org are API compatible
with .NET Standard 2.0, so in practice it unblocks many
projects.

Tooling Prerequisites

.NET Core SDK.
You always need to install .NET Core 2.0
Preview 2. This also
includes the CLI (dotnet) for building packages, so
if you only want to use the CLI, you can stop here.

Visual Studio.
If you want to use Visual Studio for authoring .NET Standard 2.0
libraries, you also need to install Visual Studio 2017
15.3. Make sure to use
15.3 and not an earlier version, as this release addressed a
couple of key issues to provide a good experience.

Visual Studio for Mac.
The latest version of Visual Studio for
Mac supports building
.NET Standard 2.0 libraries.